Electrophotographic duplicator of the transfer type

ABSTRACT

In an electrophotographic duplicator of the transfer type an image projected onto a photosensitive surface is transferred onto the surface of a transparent dielectric film superposed with respect to the photosensitive surface. The transfer is accomplished by an AC corona discharge and a uniform irradiation of the superposed dielectric film and photosensitive surface to stabilize the image. Subsequently, a transfer paper and the transparent dielectric film are superposed and the image transferred to the transfer paper by application of a toner and a corona discharge of the opposite polarity of the toner. The image on the transfer paper is then fixed by heating.

O Umted States Patent 1191 1111 3,790,273 Tanaka Feb. 5, 1974 [5ELECTROPHOTOGRAPHIC DUPLICATOR 3,084,061 4/1963 Hall 355/17 x 0]: THETRANSFER TYPE 3,166,418 1/1965 Gundlach 3,210,185 10/ 965 Olden 355/17 x[75] Inventor: Susumu Tanaka, Sakai, Japan [73] Assignee: Minolta CameraKabushiki Kaisha,

Osaka-shi, Osaka-fu, Japan [22] Filed: Dec. 29, 1971 [21] Appl. No.:213,308

[30] Foreign Application Priority Data Dec. 30, 1970 Japan 45/126791[52] U.S. Cl. 355/16 [51] Int. Cl G03g 5/02 [58] Field of Search 355/3,l7, 16

[56] References Cited lJNlTED STATES PATENTS 2,987,660 6/1961 Walkup355/3 3,308,731 3/1967 Olden 355/3 3,582,206 6/1971 Burdige. 355/33,649,117 3/1972 Weigl 355/17 then fixed by heating.

Primary Examiner1ohn M. Horan Attorney, Agent, or Firm-Watson et a1.

[57] ABSTRACT In an electrophotographic duplicator of the transfer typean image projected onto a photosensitive surface is transferred onto thesurface of a transparent dielectric film superposed with respect to thephotosensitive surface. The transfer is accomplished by an AC coronadischarge and a uniform irradiation of the superposed dielectric filmand photosensitive surface to stabilize the image. Subsequently, atransfer paper and the transparent dielectric film are superposed andthe image transferredto the transfer paper by application of a toner anda corona discharge of the opposite polarity of the toner. The image onthe transfer paper is 4 Claims, 5 Drawing Figures mm Sum M99273 sum 2 or2 F I G. 3

2 1 w? z w IOACM Mb 50H 3 I H MT c H cLw (0) (b) (c). (d) '(e)ELECTROPHOTOGRAPHIC DUPLICATOR OF THE TRANSFER TYPE BACKGROUND OF THEINVENTION The present invention relates to an improvedelectrophotographic duplicator of the transfer type for projecting anoriginal onto a photosensitive material via an optical system, formingthe electrostatic latent image on a superposed insulating transparentfilm by means of AC corona discharge, stabilizing the latent image by auniform exposure all over the surface of the photosensitive materialdeveloping the latent image by means of a dry toner developing device,and producing copies by transferring the developed figure to transferpapers by means of a transferring device.

In general a dry developing type electrostatic duplicator uses aphotosensitive material consisting of photoconductive substances such asamorphous selenium and the like mounted on a drum and around which acharging station, an exposure station, a developing station, atransferring station, and a cleaning station are arranged in the orderstated above. Thus, at the charging station the photosensitive body ischarged by a corona discharge device; at the exposure station theoriginal is exposed to the mirror image and the electrostatic latentimage is formed on the surface of the photosensitive material; at thedeveloping station the latent image is developed by means of a cascadedeveloping method or the like; and at the transferring station a drytoner developed image is transferred to transfer papers supplied fromthe paper supplying station, the transferred image being fused at theheat fixing station for producing copies. However, such a duplicator hasthe following drawbacks:

l. The framework of the duplicator is large-sized because of the largedrum.

2. Its photosensitive material may not be readily exchanged for anotherphotosensitive material.

3. The resolving power of the image is lowered because the imageexposure is made on the areshaped photosensitive material.

4. Copies produced by such a duplicator have fog because theelectrostatic latent image on the photosensitive material is developeddirectly. So the apparatus is unfit for the reproduction of an originalwith many stains on its surface.

5. Its photosensitive material has flaws on its surface because a drytoner image is formed directly on the material and the image istransferred to transfer papers.

The present invention is constructed to remove the foregoing drawbacksby forming its photosensitive material into an endless belt shape sothat it may be easily exchanged for another belt, making it possible toreceive an even image exposure thereby; superposing an insulatingtransparent film upon the photosensitive material and applying to thesuperposed material and film an AC corona discharge and uniform exposureall over the surface of the photosensitive material; forming a correctedelectrostatic latent image on the insulating transparent film; and,after dry toner developing the latent image, transferring the developedimage to transfer papers.

OBJECTS OF THE INVENTION type for forming a corrected electrostaticlatent image on an insulating film superposed upon a photosensitivematerial thereby producing a high density copy, especially for anoriginal having stains on its surface.

Another object of the invention is to provide electrophotographicduplicator of the non-contact transfer type wherein the surface of thephotosensitive body is not damaged.

Still another object of the invention is to provide anelectrophotographic duplicator of the transfer type for producing copieswhich are small-sized and yet which has high resolving power.

The above, as well as other, features and objects of the presentinvention are readily understood from the following detailed descriptionof the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1a is a side-view showing the main components of one embodiment ofthe present duplicator.

FIG. lb is a view of the driving mechanism showing the exposure opticalsystem of the slit type for one embodiment of the present duplicator.

DETAILED DESCRIPTION OF THE INVENTION In FIG. la, 1 is the framework ofthe duplicator, 2 is an original exposure station provided on the upperpart of the framework, and 3 is an endless supporter, which is shown inthe shape of a belt in the drawing, on which photosensitive material Pof the same size as the exposure station is attached. Belt 3 andphot0sensitive material P, for example as shown in FIG. 4, are of thelaminated type comprising, an organic semiconductor film ofpolyvinyl-carbazole including a thin aluminum film as an electrode, avery thin non-crystalline Se evaporated film and a small quantity ofsilicone fastened on stainless belt 3 which is 50 ,u thick length andhas a length equal to the length of the original exposure station. Belt3 is connected with motor driving source M and which is rotatedconstantly by belt 34 via electromagnetic clutch CLM, FIG. 3, and isplaced on revolving carrier-roller 4 and inverted rollers 5 and 6.Numeral 7 is a charging device consisting of a corona discharger andnumeral 8 identifies the exposure aperture of the slit type exposureoptical system 35. Exposure optical system 35 is constructed so thatrevolver D, on the second shifting base B provided with two mirrors M ismovable on a pair of guide rails G provided parallel to original 0 atexposure station 2. First shifting base A provided with originalilluminating system I and mirror M is mounted on revolver D and isconnected by a belt shiftable from one pulley to another on the externalboundary of wheel W whose internal boundary and fixed axle are connectedby spring S. By the actuation of electromagnetic clutch CLM shown inFIG. 3, wheel W is connected with a driving source (carrier-roller 4) sothat W revolves around driving source 4 relative to the revolution ofbelt 3, by means of a gear transmission and the like which are notillustrated in the drawing. Original 0 is shifted to the left in thedrawing at the peripheral speed of belt 3 while it is being illuminated.Then the second shifting base B is inverted at one half of that speedand the image of original is reflected by means of mirrors M, and M Theimage is passed through fixed projection lens L, is further reflected bymeans of fixed mirror M and is then projected on photosensitive materialP which is moved along exposure aperture 8. At the end of the scanningof the original electromagnetic clutch CLM is disengaged, wheel W isreversed by means of the accumulated force of spring S and thus shiftingbases A and B are returned to their original positions. Further, at therear part of belt 3 opposite exposure aperture 8 retaining member 9 isprovided. 10 is a correction charging device consisting of an AC coronadischarger, 11 is a white light source consisting of a tungsten lamp, 12is a developing device consisting of for example, developing rollers 13maintained at one polarity and driven by motor M and electrodes 14 atthe opposite polarity so that maintained a number of developing brushesmay be formed. 15 is a transferring device consisting of a coronadischarger, which is mounted opposite to carrier-roller 4 in FIG. 1. 16is a dielectric transparent film 10 100p. thick, made from for example apolyester, polyethylene, or vinyl chloride, which is supplied from roll31 and is wound on roll 32. During passage from charging device 10 totransferring device 15 correcting film is stretched along the belt 3 bymeans of feed roller 17 and tension roller 18 so that it may be carriedat the same speed as the shifting speed of belt 3 by being connected bypressure with photosensitive material P between rollers 4 and 6, and,also, by electromagnetic clutch CLM, shown in FIG. 3, motor M feedroller 17, and belt 34. Further, if feed roller 17 is directly connectedwith carrier-roller 4, electromagnetic clutch CLM, may be omitted.

19 denotes an AC corona discharger for removing residual charges ondielectric film 16 and 20 denotes a cleaning device, the residual tonerbeing removed by means of cleaning brush 21 driven by motor M which isnot shown in the drawing and is attracted by fan F 22 is a papersupplhing roller delivering successive sheets of transfer paper Taccumulated on base 36 by 1 the drive of motor M 23 is 'a pressureconnecting roller for placing transfer paper T on dielectric film l6superposed upon the photosensitive material at transferring device 15.24 is a conveyer'belt carrying transfer paper T to copy receiving tray25 provided outside the framework of the duplicator. Belt 24 is mountedover roller 33 connected by belt 34 with motor M and is thereby driven.26 is a heat fixing device consisting of heater H and fan F FIGS. 2A to2C show a cam mechanism using three discs each of which is of the sameradius. First cam 27 has projection 27a by which microswitch SW, isturned of (FIG. 2(A)), the second cam 28 has semicircular projection 28aby which microswitches SW and SW,, are turned on (FIG. 2(B) the thirdcam 29 has semicircular projection 29a by which microswitches SW.,, SWSW SW, and SW, are turned on (FIG. 2(C) These three cams are fixed onthe same axlein the phase relation illustrated in the drawing and areconnected via a gear transmission mechanism, which is not shown in thedrawing, with carrier-roller 4 serving as a driving source, as they arerevolved once, relative to two revolutions of belt 3. Microswitches SW,to SW for the working of each device actuated by these cams areconnected as indicated in FIG. 3.

That is, relative to a power source and power source switch S motor Mheater H in the heat fixing device, fan F AC corona discharger 19 forremoving residual charges, motor M for operating the brush of thecleaning device and fan F are connected in parallel with each other.Start switch S and relay Ry which are connected in parallel with theaforesaid components, are connected in series with each other.Microswitch SW,, which is connected in parallel with start switch S andrelay switch A of relay Ry are connected in series with each other.Electromagnetic clutch CLM, of carrier-roller 4 and electromagneticclutch CLM, of feed roller 17 are connected in parallel with each other.Microswitch SW is connected in series with charging device 7,microswitch SW is serially connected with illuminating lamp I of theexposure device and clutch CLW of wheel W, microswitch SW is seriallyconnected with corrections charging device 10, microswitch SW isserially connected with uniform exposure light source 11, microswitch SWis serially connected with driving motor M of developing roller 13 indeveloping device 12, microswitch SW is serially connected with drivingmotor M of paper supplying roller 22 of transfer paper T, andmicroswitch SW is serially connected with the corona discharger oftransferring device 15.

The operation of the present electrophotographic duplicator whosecomponents are as described above will be explained by means of the cammechanism indicated in FIGS. 2A to 2C, the circuit in FIG. 3 and thediagram in FIG. 4.

Now, when power source switch S is closed, motive motor M is driven butmicroswitch SW, is in an opened state. That is because microswitch SW isactivated by means of projection 27a of the first cam 27 and the contactsegment of microswitch SW, is mounted on projection 27a of the cam. Inthis case belt 34 is shifted but clutches CLM, and CLM, are notactuated, and carrier-roller 4 and feed roller 7 are not turned and belt3 and insulating film 16 are not shifted. Conveyer belt 24, heat fixingdevice 26, cleaning device 20 and charge removing device 19 areactuated.

At the start of duplication, when original 0 is placed on exposurestation 2 and start switch S is pushed, relay R is actuated, contactsegments A, and A, of relay Ry are closed, clutches CLM and CLM areactuated, carrier-roller 4 is turned by means of clutch CLM and thefirst cam 27, the second cam 28 and the third cam 29 which areinterlocked by gears with carrier-roller 4 are turned, and feed roller17 is turned by clutch CLM At the instant the first cam 27 is turned,the contact segment of microswitch SW, is closed and relay Ry isself-held. At the instant the second cam 28 is turned, microswitch SW isturned on, charging device 7 starts corona discharge, and photosensitivematerial P on belt 3, as shown in FIG. 4(a), is carried while beingcharged. When photosensitive material P is carried just in front ofexposure aperture 8, microswitch SW is turned on by projection 28a ofthe second cam 28. At the instant illuminating lamp l is lighted, clutchCLW of wheel W is actuated, wheel W interlocking with belt 3 is turned,exposure optical system 35 on shifting bases A and B is shifted, themirror image of original 0 is progressively projected on chargedphotosensitive material P which is passing 5. through exposure aperture8 while original is being illuminated, and an electrostatic latent imageis thus formed as shown in FIG. 4(b). After passing through inventingroller 6, photosensitive material P is pressed aginst dielectric film 16supplied from roll 31 and is superposed upon film 16 (FIG. 4(0) Whenmicroswitch SW is closed by means of projection 29a of the third cam 29,correction charging device starts AC corona discharge, an electrostaticimage, as shown in FIG. 4(d), resulting from the characteristics of theoutput current of the AC corona discharger is formed on dielectric filml6. Microswiteh SW is closed by means of projection 29a of the third cam29, light source 11 is lighted, photosensitive material P is excited andthus an electrostatic image is stabilized as shown in FIG. 4(e) ondielectric film l6 and its contrast increased. Developing device. 12 isactuated at the instant microswitch SW is turned on by means ofprojection 29a of the third cam 29 and, as shown in FIG. 4(f),dielectric film 16 is deeloped by the toner. Prior to developmentdielectric film 16 is carried with photosensitive material P totransferring device 15, microswitch SW is turned on by means ofprojection 29a of the third cam 29, one sheet of the upper-most transferpaper T, which is the last copy to be made, is delivered by means ofpaper supplying roller 22 from the transfer paper receiver andsubsequently transfer paper T is pressed against dielectric film 16 tobe superposed upon one another (FIG. 4(g) When microswitch SW is turnedon by means of projection 29a of the third cam 29, transferring device15, starts the corona discharge with a polarity opposite to the polarityof the toner image, and transfers the toner image formed on dielectricfilm 16 to the transfer paper as shown in FIG. 4(h). After the transfer,transfer paper T is separated from dielectric film 16, film 16 isseparated from photosensitive material P, material P passes throughcharging device 7 again for its second shift, the residual charge offilm 16 is removed by means of AC corona discharger 19 arranged justbehind transferring device 15, and the residual toner is wound on roll32 while being removed .by means of cleaning device 20. Transfer paper Tto which the toner image has been transferred is fixed by heat, when itpasses under heat fixing device 26 by means of conveyer belt 24, and iscarried to receiving tray 25. When photosensitive material P hascompleted one revolution and is just ahead of charging device 7,projection 28a of the second cam 28 is deactuated and switch SW isturned off, for the reason that the second cam 28 makes one-half of itsrevolution. Consequently, when photosensitive material P makes itssecond revolution, it is shifted without being charged, and when itpasses through exposure aperture 8, switch SW is turned off becauseprojection 28a of the second cam 28 is deactuated, and, whileilluminating lamp I of the afore-mentioned exposure optical system isextinguished, photosensitive material P stops moving and is returned toits original position by means of the aforementioned return spring.Thus, photosensitive material P, without being subjected to exposure, isagain superposed upon insulating film l6 and passes through connectioncharging device 10, and is carried past light source 11 and developingdevice 12, but, because projection 29a of the third cam 29 is deactuatedand switches SW SW and SW are turned off in regular sequence, no imageis made. Further, because projection 29a of the third cam 29 isdeactuated and switch SW is turned off, transfer paper T is notsupplied. Before photosensitive material P arrives at transferringdevice 15, that is, makes a revolution after the transferring operationis started, the trailing end of the transfer paper passes throughtransferring device 15 and the transferring operation is ended.Simultaneously, time switch SW is turned off because projection 29a ofthe third cam 29 is deactuated, the corona discharge of transferringdevice 15 being stopped thereby. Further, when the photosensitivematerial is shifted and arrives at its original position just beforecharging device 7, that is, when material P has made two revolutions,microswitch SW is turned off by means of projection 27a of cam 27, andthus relay Ry is self-released, clutches CLM, and CLM becomesdeactivated, photosensitive material P and dielectric film 16 beingstopped at the same time.

Accordingly, an image of an original is formed during the firstrevolution of belt 3, the image is transferred to transfer paper Tduring its second revolution and at the same time those which have beentransferred are delivered to tray 25.

Because the present electrophotographic transfer type has the structureas described above, copies produced by its image correcting means,consisting of an insulating transparent film, a charging device forcorrection of AC corona discharge and a uniform exposure light source,have no fog, are fair, and have high density, as compared with thoseproduced by dulicators heretofore known. The reason is that an image isformed by positive charge in the dark parts thereof and by negativecharge in the light parts thereof on a film, as shown in FIG. 4(e). Thepresent duplicator has the following advantages: 1) It is suitable forthe duplication of an original such as a drawing, a document, and thelike. 2) It is constructed so that there is no positive chargecorresponding to the light pants of the image on the dielectric filmbecause of the AC corona discharge as may be seen clearly from FIG.4((1), relative -to an original having stains on its surface, that is,an

original having a small quantity of negative charge in the light partsthereof as in FIG. 4( b) and as a result fair copies with no fog may beproduced. 3) Because the photosensitive material is covered with adielectric film, and is not directly developed, there is no damage tothe photosensitive material resulting therefrom 4) The photosensitivematerial withstands long and repeated use. Finally the apparatus mayutilize a photosensitive material with an elastic surface.

I claim: 1. An electrophotographic duplicator of the transfer typecomprising:

means for projecting an image of an original document at an exposurestation and including a projection lens; a slit-shaped exposure apertureprovided on the image plane of said projection lens; a photosensitivesurface of a photosensitive material formed as a flexible endless belt;a number of rollers extending said endless belt along said exposureaperture thereby forming a carrier path for said endless belt and adriving device for driving said endless belt in one direction along saidcarrier path; a first DC corona discharge device adjacent said carrierpath for uniformly charging the photosensitive surface and means forsupplying a transparent dielectric film in superposing relationship withsaid photosensitive surface;

a second AC corona discharge device adjacent said transparent dielectricfilm superposed upon said photosensitive surface for forming anelectrostatic latent image thereon corresponding to the electrostaticlatent image on said photosensitive surface and formed selectively bypositive charge or negative charge on the transparent dielectric film;

an illuminating device irradiating the whole of the photosensitivesurface through the transparent dielectric film upon which saidphotosensitive surface is superposed thereby stabilizing theelectrostatic latent image on said transparent dielectric film;

a developing device for developing the electrostatic latent image formedon said transparent dielectric film;

a device for supplying transfer paper to the surface of said developedtransparent dielectric film;

a transferring device for superposing said transfer paper upon saidtransparent dielectric film a third corona discharge device for chargingsiid transfer paper with a charge of opposite polarity as the polarityof said toner and transferring an image corresponding to the originalimage;

a transfer paper carrier path separating the transfer paper passedthrough said transferring device from the transparent dielectric filmpath and a transparent dielectric film carrier path separating thetransparent dielectric film from the photosensitive surface; and

a heat fixing device mounted adjacent said transfer paper carrier path.

2. An electrophotog'raphic duplicator as in claim 1 further comprising:

wherein said number of rollers comprise a first roller and a secondroller mounted parallel to said exposure station, said second roller isa carrier roller corresponding to said transferring device and saidtransparent dielectric film is superposed upon the photosensitivesurface and carried together between said first and second rollers; and

said second AC corona discharge device facing said carrier path. 4. Anelectrophotographic duplicator as in claim 3 wherein said number ofrollers comprises a third roller, the carrier path between said firstroller and said third roller faces said exposure station, and said firstDC corona discharge device is mounted facing the carrier path betweensaid second roller and said third roller.

1. An electrophotographic duplicator of the transfer type comprising:means for projecting an image of an original document at an exposurestation and including a projection lens; a slit-shaped exposure apertureprovided on the image plane of said projection lens; a photosensitivesurface of a photosensitive material formed as a flexible endless belt;a number of rollers extending said endless belt along said exposureaperture thereby forming a carrier path for said endless belt and adriving device for driving said endless belt in one direction along saidcarrier path; a first DC corona discharge device adjacent said carrierpath for uniformly charging the photosensitive surface and means forsupplying a transparent dielectric film in superposing relationship withsaid photosensitive surface; a second AC corona discharge deviceadjacent said transparent dielectric film superposed upon saidphotosensitive surface for forming an electrostatic latent image thereoncorresponding to the electrostatic latent image on said photosensitivesurface and formed selectively by positive charge or negative charge onthe transparent dielectric film; an illuminating device irradiating thewhole of the photosensitive surface through the transparent dielectricfilm upon which said photosensitive surface is superposed therebystabilizing the electrostatic latent image on said transparentdielectric film; a developing device for developing the electrostaticlatent image formed on said transparent dielectric film; a device forsupplying transfer paper to the surface of said developed transparentdielectric film; a transferring device for superposing said transferpaper upon said transparent dielectric film a third corona dischargedevice for charging siid transfer paper with a charge of oppositepolarity as the polarity of said toner and transferring an imagecorresponding to the original image; a trAnsfer paper carrier pathseparating the transfer paper passed through said transferring devicefrom the transparent dielectric film path and a transparent dielectricfilm carrier path separating the transparent dielectric film from thephotosensitive surface; and a heat fixing device mounted adjacent saidtransfer paper carrier path.
 2. An electrophotographic duplicator as inclaim 1 further comprising: an AC corona discharge device mountedadjacent the carrier path of the transparent dielectric film separatedfrom the endless belt on which the photosensitive surface is formed forremoving residual charges therefrom; and a cleaning device for cleaningsaid transparent dielectric film.
 3. An electrophotographic duplicatoras in claim 1 wherein said number of rollers comprise a first roller anda second roller mounted parallel to said exposure station, said secondroller is a carrier roller corresponding to said transferring device andsaid transparent dielectric film is superposed upon the photosensitivesurface and carried together between said first and second rollers; andsaid second AC corona discharge device facing said carrier path.
 4. Anelectrophotographic duplicator as in claim 3 wherein said number ofrollers comprises a third roller, the carrier path between said firstroller and said third roller faces said exposure station, and said firstDC corona discharge device is mounted facing the carrier path betweensaid second roller and said third roller.